Cyanide process of treating ores of the precious metals



D. L. H. CYAHDE PROCESS 0F THEA'HNG OP. Awncmxm: mi

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i Patented @tu 3,'l922.

DAVID L. H. FORBES, OIE' KIRKLAND LAKE, ONTARIO, CANADA.

CYANIDE PROCESS OF, TREATING CRES 0F THE PRECIOUS Application led April 3,

Be it kno n that I. Dxvn) L. H. FORBES, of Kirkland Laike, in the district of rIimiskamingr` Province of Ontario, Canada, a subject of the llinpA of Great Britain, have invented certain new and useful Improvements in Cyanide Processes of Treating Orcs of the Precious Metals, of which the following is a spcciiication. t

This invention relates to the treatment of ores of the precious metals, and more particularly ores containing Vtellurides of the precious metals, by the well known cyanide process.

When unroasted ores containing such tellurides are treated according to the most approved modern practice, the loss is often as much from 15% to 20% of the gold present, whereas with ordinary ores it is possible, economically to recover all but 3% to 4% of the gold.l My object therefore is to devise an economically practicable method of increasinp` the recovery of precious metals from ores containing tellurides. The essentials, chemically, of such a process seem to be the presence in the ore pulp of nascent oxygen, strong caustic. and aV minimum of cyanide. A further physical essential is that the nascent oxygen be generatedin such a manner that it docs not escape from the pulp until .it has had Jfull opportunity of coming into intimate contact with the ore particles.

I attain the desired conditions both chemically and physically by injecting pouf'dered sodium peroxide beneath the surface ofa mixture of the 2ground orc and cyanide solu tion, preferably by means of the action of a blast ot compressed air.

.'Xpparatus adapted for this purposc is shown in the accompanying drawinggwhich is a side elevtion of the apparatus, partly broken away.

1 is a tank adapted to contain a mixtureV of comminuted orc and cyanide solution. Above the tank is suitably supported a re cepta'cle 2 for the powdered sodium peroxide. This is provided with asuitable cover such las a screw cap The lower end of the receptacle is provide'd with a discharge pipe 4, which extends downwardly to4 a position well below the normal surface level of the contents of the tank. A, compressed air pipe 5 is led from a suitable source of compressed air and opens through the side of thereccptacle 2, preferably just above the outlet 1922. Serial No. 549,307.

.the pipe it, not only' is sodium peroxide thus delivered to a point Well below the surface of the material in the tank, but the air, which is used to feed the peroxide, also serves either alone or with the air of any ,mechanical adjuncts to effect the necessaryagitation of tue pulp.

A moisture trap 9 of any known type is preferably inserted in the pipe 5 to take moisture out of the air, which otherwise would tend to break up the peroxide before it. reached its proper point of application.

In the practical application'ojf .my process I follow the usual' practice of reducing the ore and grinding it in cyanide solution until the desired degree of iineness is reached, and of treating the ground ore in agitation tanks. My process, howevendilfers from that cornmonly employed in that into one or more of the agitation tanks, or at some other convenient stage in the process I inject sodium peroxide by means of the apparatus hereinbefore described or by any other means.' vFrom this it results that nascent oxygen liberated by the action of the liquid on the sodium peroxide, as well as ithe resulting strong caustic soda solution, comes into intimate contact with the line particles of ore before the. oxygen has a chance to escape from the moisture. While I have found thata continuous injection of sodium peroxide at aA uniform rate gives the best results, I have also found that intermittent injection is beneficial. In practiceIhave found that the injection of sodium peroxide `in proportions even as smallfas one-,quarter of a pound of sodium peroxide per ton of yore treated gives `an increased recovery greater than the cost ofthe treatment. @n average ores one-half of a pound of sodium peroxide per ton may he used to. advantage, while, on rich ores, proportions as much as three to five pounds per ton or more may be used to advantage, yit being necessary, however, to keep in mind the fact that the upper limit would be set in practice by the percentage of caustic soda that could v'he carried safely in the solution Without interfering with Lthe subsequent Settling, iiltering or precipitation operations.'

A Jfurther beneit resulting from my pro-` cess lies in the changed character of the goldsilyer-zinc precipitate that is obtained from the pregnant. solution. When treating telluride ores, 'as above described, l have found that there is avery marked decrease in the proportion of tellurium present in this precipitate and that the ture of ore inthe cyanidesolution and preferably by means oi' compressed air.

llVhat ciaim as my invention is z- 1. The lprocess of treating orescontaining precious metals which consists in injecting small quantities of dry sodium peroxide belou1 the surface of la mixture of comminuted ore and cyanide solution.

2. The process of treating ores containing precious metals which consists in injecting small quantities of dry sodium peroxide helow the 'surface of a mixture of coinminuted ore and cyanide solution with andv by means of compressed air. l

3. The process of treating reractory ores volatilization loss. of gold when melting the precipitate into bul' of the precious metals containing tellurides of goldor silv'er which consists in introduc- 40 ing small quantities of dry sodium peroxide into a mixture of comminuted ore and cya- K vnide4 solution.

4. The process of treating refractory ores 'of the precious metals containing'tellurides 45 of gold or silver which consists in injecting' small quantities of dry sodium peroxide below the surface of a mixture otcomminuted ore and cyanide solution.

5. The process of treating ores containing precious metals which consists in injecting small quantities of dry sodium peroxidelbelou7 the surface of a mixture of comminuted ore and cyanide solution and thoroughly agitating the mixture.

. 6. The process of'treating refractory ores 'of the precious metals containing telluridesv I of gold or silver which consists in introducing small quantities of dry sodium peroxide into a 'mixture of comminuted ore and cya- 60 nide solution and 'thoroughly agitating the mixture.

7. The process of treating refractory ores of the precious metals containing tellurides of gold or silver which consists in injecting Asmall quantities of dry sodium peroxide oelow thesurface of a mixture of comminuted ore and cyanide solution with and by means of compressed air. p

Signed at ,Kirkland Lake this 25th day 70 of March 1922.

DAVID L. H. FORBES.

y vWitnesses:

M. DE Lrsnn, l L. A. Linmon. 

